Executive Summary

Group 7 dissected a small four-stroke Tecumseh lawnmower engine. Operation of the engine begins with the pull start, which turns the flywheel. When it is spinning, the magnetic plate in the flywheel generates current through the electromagnet, which passes to the spark plug. This creates an arc across the spark plug’s gap, igniting the compressed fuel/air mixture inside the engine. The explosion moves the piston, which rotates the crankshaft. A gear on the crankshaft engages with the camshaft, which turns the mower blades.

The group received the engine broken and was not able to fix it, though it is in better condition than when we started. Initially, there were portions of the throttle assembly and a key shoved in to the engine instead of being assembled in their correct places (see Fig 1.9b). There were quite a few cracks and broken pieces, including on the flywheel head and the cylinder head. The starter did not engage. Although it has been reassembled better than it was received, the engine will never be able to run because it has too many broken pieces.